CA1218004A

CA1218004A - Flexible transparent sheet made of synthetic material

Info

Publication number: CA1218004A
Application number: CA000419950A
Authority: CA
Inventors: Hans G. Brunion; Christian Hiemenz; Hans Heuser; Helmer Raedisch
Original assignee: Saint Gobain Vitrage SA
Current assignee: Saint Gobain Vitrage SA
Priority date: 1982-01-22
Filing date: 1983-01-21
Publication date: 1987-02-17
Also published as: EP0085006A2; JPS58171953A; BR8300300A; ES519116A0; EP0085006B1; DE3201849A1; DE3367878D1; JPH0243627B2; ES8308760A1; US4540622A; ATE23822T1; EP0085006A3

Abstract

ABSTRACT OF THE DISCLOSURE

A flexible transparent sheet made of a syn-thetic material is used as a flexible rear window in the folding top of a convertible; the sheet is formed of a multi-layer foil consisting of a thin core-layer, at the most about 1 mm thick and made of an impact-and-tear resistant synthetic material, and of covering layers between 0.2 and 0.5 mm thick and made of highly resili-ent polyurethane with self-healing properties.

Description

The invention relates to a flexible trans-parent sheet made of a synthetic material, more particu-larly for use as a flexible, foldable rear window in the folding top of a convertible.
Various partly conflicting demands are made upon such sheets. On the one hand, the sheets must have satisfactory optical properties to ensure that they do not distort the view; they must also be sufficiently rigid, so that they are as free as possible from waves when they are under tension, i.e. when the top is closed. On the other hand, a sheet of this kind must be sufficiently flexible so that, since it is a part of a convertible top, it can follow the folding operation without buckling. The sheet of synthetic material must also be sufficiently resistant to scratching to ensure that the view through it is not impaired by a scratched surface. Finally, these properties must be retained over a long period of time and at high and low tempera-tures, i.e. between + 80 and - 40C.
As yet no known sheet meets all of these requiremen s optimally. In particu]ar, if the optical properties are satisfactory, flexibility leaves much to be desired and, furthermore, in the case of all known plastic rear windows, surface scratch-resistance is relatively poor, with the result that, especially after long use, the surfaces are affected to a greater of lesser degree, thus impairing transparency. This ~2~

applies in par~ic~llar to windows made of soft PVC about 1.5 mm in thickness.
It is the purpose of the invention to provide a plastic sheet which is flexible and is suitahle for use as a rear window in a foldable convertible top and for other similar applications, the sheet to be re-siliently deEormable to a high degree and to be highly resistant to scratching and abrasion. Furthermore, these properties are to be retained over a long period of time and o~er an extended temperature range of between about - 40 and + 80C.
The sheet according to the invention is characterized in that it is in the form of a multi-layer foil consisting of a core-layer at the most about 1 mm in thickness and of covering layers between 0.2 and 0O5 mm in thickness made out of highly resilient, impact-and scratch-resistant polyurethane with self-healing properties.
Multi-layer foils having these properties possess a seri4s of advantages making them particularly suitable for use as foldable rear windows and for the like applications. Among these are high flexibility, high resistance to scratching and heat on the part of the self-healing covering layers, excellent process-abiiity of the laminated foil, and satisfactory be-haviour in use over long periods of time. It has furthermore been found that the sheets according to the ~ 3 invention may easily be sewn into the opening for the window made in a piece of fabric. On the one hand, the core-layer provides the necessary resistance to tearing, while the resilient covering layers ensure that the holes made by the needle close up again to prevent the entry of humidity and water. Whereas the external covering layer of the fitted window provides protection against scratching by external factors such as cleaning and ice-removal, the internal self-healing covering layer protects the window against damage by abrasion to which this surface is exposed when the top is folded and the folds in the window are caused to rub against each other by vibration as the car is being driven. In addition to this, it was found that the extremely soft, highly resilient covering layers also facilitate the actual folding procedure.
The windows according to the invention are suitable not only for convertible tops but also for all similar applications, for example windows in truck tarpaulins, in tents and in sailing boards.
The covering layers made of highly resilient polyurethane with self-healing properties may be applied by various methods pertaining to the state of the art.
This includes known spraying and immersion methods.
According to one example of embodiment, the core-layer is made of polycarbonate foil between 0.3 and 0.8 mm in thickness, while the covering layers, made of C~ L/~
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highly resilient polyurethane with self-healing proper-ties, are each about 0.4 mm in thickness.
Acco.rding to another example of embodiment, the core-layer consists of a foil~ between 0.2 and about 1 mm in thickness, made of polyurethane-urea which is relatively soft as compared with polycarbonate, the polyurethane-urea having a predominantly linear molecu-lar structure and aliphatically or cycloaliphatically bonded urethane- and urea-segments. Polyurethane-ureas of this kind are produced by reacting a prepolymer con-taining isocyanate groups with aliphatic or cyclo-aliphatic primary diamines having an average molecular weight of 60 to 240. The prepolymer containing i50-cyanate yroups is made from a polyester-diol or a polyether-diol having an average molecular weight of 500 to 4000/ or from a mixture of such polyester and polyether-diols, frorn shoxt-chained aliphatic diols having molecular weights of 62 to 250, and from an excess, in relation to the free hydroxyl groups, of an ~ aliphatic or cycloaliphatic diisocyanate.
In the drawing Figure 1 represents a window in the form of a multi-layer foil comprising a thin core-layer 1 made of a plastic resisting to shocks and tears and covering layers 3 of a highly resilient poly-urethane with self-healing properties bonded to -the core-layer 1 by adhesive layers 2.

- 4a -Preferred examples of embodiment of a lami-na-ted foil according to the invention are described hereinafter in de~ail in conjunction with the drawing attached hereto.

Core-layer 1 consists of a clear, transparent polycarbonate foil 0.5 mm in thickness, for example a /

q~

commerciall~ available foil known as LEXAN (trademark) produced by General Electric. Applied to each side of this polycarbonate foil is a covering layer 2, 0.4 mm in thickness in the form of a foil attached permanently to the core-layer by a layer of adhesive 3 about 0.02 mm in thickness.
The covering~layer foil is produced in a manner known per se, in that a solvent-free, homoyene-ously mixed reaction-casting-resin, of the composition described in German Patent 2 452 92~, is cast, with the aid of a wiping-casting-head, onto an optically perfect casting base, for example a sheet of glass, in the form of a layer 0.~ mm in thickness which then polymerizes, if necessary under the action of heat. The layer of adhesive, in the form of a solution is then poured onto the polymerized layer, again by means of a wiping-casting-head. After the solvent has evaporated, the double-layer covering foil is removed from the casting base. The production of such an adhesive-coated cover-ing foil is described in detail in German AS 2 629 779.
The double-layer covering foil thus produced is applied in a manner known per se by using heat and pressure, for example by means of a laminating roller, with simultaneous or subsequent heating of the lami-nation to a temperature of about 120 C.
If a tinted window is to be produced, the finished lamination is immersed in a tinting solution -- 6 ~

whereby the desired tint is applied to the covering layers. A method of this kind for tintirlg covering layers is describea in French Patent Application

2 467 908, Published May 15, 1981, to which reference is made in this connection.

A foil made of a thermoplastic polyurethane-urea 0.6 mm in thickness is used as the core-layer, the polyurethane-urea being produced as follows:
- lO00 g of a linear polyester, obtained by reacting adipic acid with tetramethylene-glycol, having an average moleculax weight of about 2250 and contain-ing about 1.5% of free O~ groups, are gasified with nitrogen, after vacu~lm-drying at 0.02 bars and 110C, and are cooled down to about 80C under this protective-gas atmosphere. 496 g of isophorone-diisocyanate, containing about 37.5~ of free NCO
groups, are then added to this melt and the mixture is converted, at a temperature of about 90C, to an NCO-containing prepolymer. After about 3 hours, 121 g of tetramethylene-glycol are added for pre-liminary chain-lengthening, the temperature being increased to 120C for l hour. 1.5 litres of xylene are then added to the prepolymer melt thus obtained.
After cooling to about 30C, 73 g of isophorone-diamine are added to the solution to complete the chain-len~thening. An optically satis~actory filmed -i ~- 7 --is obtained from the resulting highly viscous, clear solution by pouring i,t onto sheets of glass and subsequently evaporating the solvent.
A castable reaction-mixture is then produced as follows:
- 1000 g of a polyether produced by reacting propylene-oxide with a triol, for example glycerin or trimethyl-propane, and having a molecular weight of about 450 and containing between 10.5 and 12% of free OH groups, - 0.5 g of dibutyl-tin-dilaurate, - 1000 g of a biuret or triisocyanurate of 1,~-hexamethylene-diisocyanate containing between 21 and 24% of free NCO groups, and - 30 g of bis(l,2,2,6,6-pentamethyl-4-piperidyl)-sebacate, - 20 g of 2-(2-hydroxy-3,5-di-tert-amylphenyl~-2H-benztriazole are mixed homogeneously in a vessel under negative pressure. With the aid of a wiping-casting-unit, this castable reaction-mixture is cast consecutively onto the two surfaces of the core-layer, to form a layer 0.5 mm in thickness. The cast layers are allowed to polymerize by the action of heat. Instead of this, foils of about 0.5 mm in thickness may be produced from this reaction mixture by the pouring method, the foils being laminated directly to the two surfaces of the core-layer by the use of heat ~nd pressure.
Since the self-healing layers are exposed directly to solar radiation, it is desirable to add a light-stabilizer and a UV-absorber to the reaction-mixture. Chemical compounds from the class of steri-cally hindered amines, for example bis(2,2,6,6-tetra-methyl-4-piperidyl~-sebacate, or bis(l,2,2,6,6-penta-methyl-4-piperidyl)-sebacate have been found particu-larly suitable as light stabilizers. These light-stabilizers are added to the reaction-mixture in amounts of up to 9% of the ready-to-cast reaction-mixture.
Optimal UV-stability results are obtained by adding about 5~, but even smaller amounts, of the order of 1%, produce qui~e satisfactory results. In addition to the light-stabilizer, the use of a UV-absorber has been found desirable, the amounts involved being between 0.1 and 5% by weight. The addition of about 1% by weight, in relation to the ready-to-cast reaction-mixture, of 2-(2-hydroxy-5-methylphenyl)-2H-benztriazole, for example, has been found to provide satisfactory UV-absorption.

The procedure for producing an electrically heatable, foldable rear window is as follows: a thermo-plastic polyurethane-urea foil 0.6 mm in thickness-is produced as described in Example 2. Electrical heating conductors are embedded superficially into this core-.- 9 -layer with the aid of an apparatus such as that de-scribed in German AS 1 679 930. Instead of using wires, heating conductors in the form of a printable conducting paste may be applied to the surface of the core-layer by a printing method, for example the silk-screen process.
Suitable printable conducting pastes are commercially available. The heating wires or conductors are fitted with current-connecting elements or wires which connect the heating resistance to the power-source. After the heating resistance has been arranged upon the core-layer, the two surfaces of the latter are coated with highly resilient polyurethane layers 0.5 mm in thick-ness, by the method described in Example 2.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A flexible transparent sheet made of a synthetic material, characterized in that said sheet is in the form of a multi-layer foil consisting of a thin core-layer; at the most about 1 mm in thickness and made of an impact- and tear-resistant synthetic material, and of covering layers between 0.2 and 0.5 mm in thickness and made of a highly resilient polyurethane with self-healing properties.

2. A flexible transparent sheet according to Claim 1, characterized in that the core-layer consists of a polycarbonate foil between 0.3 and 0.8 mm in thickness.

3. A flexible transparent sheet according to Claims 1 and 2, characterized in that the core-layer, made of polycarbonate, is about 0.5 mm in thickness, while the covering layers are made of highly resilient polyurethane with self-healing properties and are each about 0.4 mm in thickness.

4. A flexible transparent sheet according to Claim 1, characterized in that the core-layer consists of a foil between 0.2 and 1.0 mm in thickness made of a polyurethane-urea with a predominantly linear molecular structure and aliphatically or cycloaliphatically bonded urethane- and urea-segments.

5. A flexible transparent sheet according to Claim 4, characterized in that the polyurethane-urea is produced by reacting a prepolymer containing isocyanate groups with aliphatic or cycloaliphatic primary diamines of an average molecular weight of between 60 and 340, said prepolymer being made from a polyester-diol or a polyether-diol of average molecular weights of between 500 and 4000, or from a mixture of such polyester and polyether-diols, from short-chained aliphatic diols with molecular weights of 62 to 250, and from an excess, in relation to the free hydroxyl groups, of an aliphatic or cycloaliphatic diisocyanate.

6. A flexible transparent sheet according to Claims 1, 2 or 4, characterized in that the covering layers consist of highly resilient polyurethane pre-fabricated foils with self-healing properties.

7. A flexible transparent sheet according to Claims 1 and 2, characterized in that the covering layers, made of a highly resilient polyurethane with self-healing properties, are united with the poly-carbonate core-layer by means of an adhesive layer made of thermoplastic polyurethane.

8. A flexible transparent sheet according to Claim 4, characterized in that the covering layers and the core-layer are united by the use of heat and pressure.

9. A flexible transparent sheet according to Claims 1, 2 or 4, characterized in that the covering layers of highly resilient polyurethane are produced by coating the core-layer with the castable reaction-mixture and are united with the core-layer.

10. A flexible transparent sheet according to one of Claims 1, 2 or 4, characterized in that highly resilient covering layers are provided with a light-stabilizer and a UV-absorber.

11. A flexible transparent sheet according to one of Claims 1, 2 or 4, characterized in that electri-cal-heating conductors are arranged in one of the layers of the laminated foil.

12. A flexible transparent sheet according to one of Claims 1, 2 or 4, characterized in that one or more of the layers in the laminated foil is tinted.